Prussic acid poisoning is caused by a poison called cyanide that can be produced in several types of plants under certain growing conditions. All species of farm animals can be affected with this acute poisoning. The plants most commonly involved in prussic acid poisoning are johnsongrass, sudangrass, common sorghum, arrowgrass, black cherry, chokecherry, pin cherry, and flax. Johnsongrass is the most toxic of the sorghums and commonly causes poisoning when subjected to frost or drought conditions. Very young, rapidly growing plants also are more likely to produce the poison. Feeding or grazing of these forages should be delayed until they are more mature. Feeding forages following heavy nitrogen fertilization, plant injury by trampling, or stunting of plant growth due to adverse weather should be avoided. If large amounts of forages containing prussic acid are eaten, death can occur within a few minutes. Excess salivation, difficult breathing, muscle tremors, and rapid heart rate all signal the onset of prussic acid poisoning. Shortly after these symptoms are seen, the animal may go down, and death will likely occur due to respiratory paralysis. Animals that live one to two hours after the onset of these signs will usually recover. Prussic acid is quite volatile, and there is little danger from feeding well-cured hay.
In addition, in some areas of the United States, johnsongrass is deemed a noxious weed. If it is found growing on one's property, a fine can be levied against the property owner.
